Solubility, lignin in wood

Determination of Acid-Soluble Lignin in Wood and Pulp... 

Technical Association of the Pulp and Paper Industry, Atlanta, (1985b) Acid-soluble lignin in wood and pulp. Useful Method UM 250... 

The support for a chemical linkage between cellulose and lignin in wood, presented by Hibbert and co-workers (90), is based on their treatment of oak wood with acetic anhydride, glacial acetic acid and catalytic amounts of sulfuric acid. A fraction soluble in dioxane was found to have, after several precipitations, the same composition of lignin, cellulose and pentosan as that of the wood itself. 

Evidence supporting the original paradigm of lignin in wood as a random, three-dimensional network polymer is reviewed. More recent results which do not fit this simple picture are discussed. A modified paradigm is proposed in which lignin in wood is comprised of several types of network which differ from each other both ultrastructurally and chemically. When wood is deligni-fied, the properties of the macromolecules made soluble reflect the properties of the network from which they are derived. 

Schuerch C (1952) The solvent properties of liquids and their relation to the solubility, swelling, isolation and fractionation of lignin J Am Chem Soc 74 5061-5067 Scott JAN, Procter AR, Fergus BJ, Goring DAI (1969) The application of ultraviolet microscopy to the distribution of lignin in wood Description and validity of the technique Wood Sci Technol 3 73 - 92... 

Schoning AG, Johansson G (1965) Absorptiometric determination of acid-soluble lignin in semichemical bisulfite pulps and in some woods and plants Sven Papperstidn 68 607-613 Schultz TP, Templeteon MC, McGinnis GD (1985) Rapid determination of lignocellulose by diffuse reflectance Fourier transform infrared spectrometry Anal Chem 57 2867- 2869 Sjostrom E, Enstrom B (1966) Spectrophotometnc determination of the residual lignin in pulp after dissolution in cadoxene Sven Papperstidn 69 469-476... 

A primary objective of wood pulping is to separate lignin from cellulose. Two chemical processes are commonly used to achieve this, namely the sulfite and the sulfate methods (Kraft-process). In the sulfite process, the lignin in wood is sulfo-nated with aqueous solutions of sulfites or hydrogen sulfites, with added SO2, at high temperatures, so that soluble lignin sulfonic acids are produced, which can be dissolved out of the wood. The sulfate method uses sodium hydroxide, sodium sulfide and sodium carbonate as basic pulping chemicals. It derived its name from the small amounts of sodium sulfate which are added to balance out alkali losses. 

Since the reason for the limited degree of delignification reached on heating wood with water or with buffer solution may be the low solubility of lignins in water, wood meal was heated with mixtures of phosphate buffer and dioxane (Fig. 6). 

Isolation and Ozonization of Lignin. The wood meal of white birch (Be-tula papyrifera Marsh.) was steamed for 15 min at 180°C, and extracted with water at 60°C, followed by extraction with methanol as shown in Figure 2. The methanol-soluble part was dried under vacuum after removal of methanol. The yield of methanol extract was 75% based on the amount of lignin present in the original wood. 

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